The present invention relates generally to machine tools, and more particularly to a cutting tool fabricated from a heavy metal material for use with heat shrink fittings.
As is well known, various tool holders have been utilized in the prior art which interface with a rotating spindle of a machine, such as a milling or boring machine, to securely hold a cutting tool upon the machine during the cutting of a work piece. In most prior art tool holders, a central opening is formed therein for receiving the shank portion of the cutting tool which is to be interfaced to the milling or other machine. Subsequent to the insertion of the shank portion of the cutting tool into the central opening, the tool holder is drawn or pulled tightly into the spindle so as to rigidly maintain the cutting tool within the tool holder.
However, prior art tool holders suffer from deficiencies related to the manner in which the shank portion of the cutting tool is secured within the central opening of the tool holder, with such deficiencies often resulting in non-concentric mounting of the cutting tool within the tool holder. Such non-concentric mounting is extremely undesirable, particularly in modern, high tolerance machining applications such as those performed on a vertical milling machine wherein minor variations in the concentricity of the cutting tool within the tool holder often times results in extreme flaws in the cutting operation. Additionally, prior art tool holders suffer from imbalances often associated with the mounting method of the tool in the tool holder thereby resulting in undesirable oscillations of the cutting tool upon the workpiece.
Recently, heat shrink tool holders have gained popularity in high tolerance machining applications for their ability to mount a cutting tool concentrically within the tool holder. In such holders, the central opening is sized slightly smaller than the diameter of the shank of the cutting tool. The cutting tool is only insertable into the central opening when the tool holder has been heated to a temperature necessary to expand the central opening to a size which can accept the cutting tool shank. Subsequent to the insertion of the shank thereinto, the central opening is allowed to cool to ambient temperature, thereby thermally contracting and rigidly maintaining the cutting tool shank within the tool holder. When using a heat shrink tool holder, it is necessary that the shank of the cutting tool be machined to exacting tolerances to enable retention within the central opening of the tool holder.
In certain machining applications, it is necessary to use diamond or carbide burr cutting tools which exhibit aggressive cutting properties and therefore are ideally suited for machining very strong metals and composite materials. Such cutting tools typically comprise a shank which is made of tool steel and includes a cutting head consisting of diamond or carbide burr deposited on one end by a very high temperature deposition process. However, this high temperature deposition process can change the thermal characteristics of the tool steel shank and alter its diameter such that it is not maintained within the exacting tolerances necessary for use with heat shrink tool holders and fittings. Therefore, in order to use a conventional diamond/carbide burr cutting tool with a heat shrink tool holder, the shank typically needs to be machined to the correct diameter after deposition of the diamond or carbide burr due to the high temperature deposition process changing the diameter of the shank and/or creating inconsistencies therein. This follow-up machining is an expensive and time consuming process which is not preferred.
The present invention addresses the deficiencies in prior art cutting tools by providing a carbide/diamond burr cutting tool that is fabricated from a heavy metal material such that the use of a high heat deposition process in relation thereto will not affect the dimensions of the tool shank, thus allowing the cutting tool to be used with heat shrink fittings and tool holders without conducting secondary machining and/or grinding operations during the fabrication process.
In accordance with the present invention, there is provided a cutting tool for use with a heat shrink tool holder or fitting. The cutting tool comprises a generally cylindrical shank which is of a selected diameter and is fabricated from a heavy metal material. Preferred heavy metal materials include, but are not necessarily limited to, tungsten, tungsten carbide, or a tungsten alloy. The heavy metal material from which the shank is preferably fabricated is capable of maintaining the selected diameter to within about 0.0003 inches despite being subjected to extremely high temperatures and subsequently cooled.
The present cutting tool further comprises an abrasive material which is secured to a portion of the shank, and more particularly to one end of the shank. The abrasive material is preferably a diamond or carbide burr, with the process of securing the abrasive material to the shank being accomplished by heating the shank to a prescribed temperature which is typically extremely high. Advantageously, the fabrication of the shank from the heavy metal material effectively maintains the diameter thereof within a prescribed range despite the heating of the shank to the prescribed temperature during the process of securing the abrasive material thereto.
The cutting tool of the present invention may be used in combination with a heat shrink tool holder or fitting which is fabricated from a thermally expandable material and includes a central opening sized to have a diameter slightly smaller than the diameter of the shank which is The heavy metal material of the shank has a coefficient of thermal expansion substantially less than that of the thermally expandable material of the heat shrink tool holder or fitting. The application of a heat source to the heat shrink tool holder or fitting facilitates the thermal expansion of the diameter of the central opening, thus allowing the shank to be slidably inserted thereinto. Subsequent to the slidable insertion of the shank into the enlarged central opening, the heat shrink tool holder or fitting is cooled to ambient temperature thereby facilitating the thermal contraction thereof (i.e., a reduction in the diameter of the central opening) about the shank of the cutting tool, thus rigidly securing the cutting tool within the heat shrink tool holder or fitting. Due to the coefficient of thermal expansion of the heavy metal material from which the shank is fabricated being substantially less than that of the thermally expandable material of the heat shrink tool holder or fitting, the reapplication of heat to the heat shrink tool holder or fitting facilitates the re-expansion of the diameter of the central opening without expanding the diameter of the shank, thus allowing the shank to be easily removed from therewithin.
Further in accordance with the present invention, there is provided a method for securing a cutting tool such as a burr tool to a heat shrink tool holder which is fabricated from a thermally expandable material and includes a circularly configured central opening. The method comprises the initial step of providing a tool having a generally cylindrical shank which is of a selected diameter that is slightly larger than the diameter of the central opening of the heat shrink tool holder, and is fabricated from a heavy metal material having a coefficient of thermal expansion substantially less than that of the thermally expandable material of the heat shrink tool holder. Thereafter, the heat shrink tool holder is heated so as to facilitate the thermal expansion of the central opening to a diameter whereby the shank of the tool is slidably insertable thereinto. The shank of the tool is then inserted into the central opening, with the heat shrink tool holder then being cooled to ambient temperature. Such cooling facilitates the thermal contraction of the heat shrink tool holder about the shank, thus rigidly securing the tool to the tool holder. The tool is removable from the heat shrink tool holder by reapplying heat to the tool holder whereby the central opening thermally expands and the tool is slidably removable from therewithin.